A major objective of this project is to investigate and exploit empty viral capsids and incomplete particles of subgroup B human adenoviruses. Research emphasizes in vitro studies of adenovirus assembly, especially with regard to DNA packaging. We wish to elucidate mechanisms of sequential protein-DNA interaction which result in compaction of viral DNA within the confines of the viral capsid. The mechanism which determines the left end polarity of DNA: capsid association in vivo is also under investigation. The transfection potential of an effective in vitro system for DNA packaging is of immediate interest. Parallel investigations of the biological activity of incomplete adenovirus particles are also underway. Particular attention is given to the abortive infections of permissive and non-permissive cells by these particles which contain DNA segments from the left end, transformation active region of the viral genome. A second objective in this project is to develop methods for physical mapping and manipulation of viral genomes. Studies of the branch migration process in products of DNA reassociation have been productive in the previous year and our present objective is to use the results for physical mapping of branch structures by electron microscopy. Stabilization of the branched structures using intercalating drugs has been demonstrated and we are interested in using these methods to permit excision of branch or loop regions from otherwise duplex DNA molecules.